Systems, devices, and methods for driving an analog interferometric modulator

ABSTRACT

This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for accurately positioning a movable conductive layer of a reflective display element. In one aspect, an initial position of the movable conductive layer with respect to at least one or more fixed conductive layers is sensed. A charging voltage may be determined based at least in part on the initial position. The charging voltage may be applied to the movable conductive layer.

TECHNICAL FIELD

This disclosure relates to driving schemes and calibration methods foranalog interferometric modulators, and for detecting the position of amovable conductor disposed between two conductors of a display element.

DESCRIPTION OF THE RELATED TECHNOLOGY

Electromechanical systems include devices having electrical andmechanical elements, actuators, transducers, sensors, optical components(such as mirrors) and electronics. Electromechanical systems can bemanufactured at a variety of scales including, but not limited to,microscales and nanoscales. For example, microelectromechanical systems(MEMS) devices can include structures having sizes ranging from about amicron to hundreds of microns or more. Nanoelectromechanical systems(NEMS) devices can include structures having sizes smaller than a micronincluding, for example, sizes smaller than several hundred nanometers.Electromechanical elements may be created using deposition, etching,lithography, and/or other micromachining processes that etch away partsof substrates and/or deposited material layers, or that add layers toform electrical and electromechanical devices.

One type of electromechanical systems device is called aninterferometric modulator (IMOD). As used herein, the terminterferometric modulator or interferometric light modulator refers to adevice that selectively absorbs and/or reflects light using theprinciples of optical interference. In some implementations, aninterferometric modulator may include a pair of conductive plates, oneor both of which may be transparent and/or reflective, wholly or inpart, and capable of relative motion upon application of an appropriateelectrical signal. In an implementation, one plate may include astationary layer deposited on a substrate and the other plate mayinclude a reflective membrane separated from the stationary layer by anair gap. The position of one plate in relation to another can change theoptical interference of light incident on the interferometric modulator.Interferometric modulator devices have a wide range of applications, andare anticipated to be used in improving existing products and creatingnew products, especially those with display capabilities.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in an apparatus for driving a display element, thedisplay element including a movable conductive layer and one or morefixed conductive layers. The apparatus includes a circuit configured todetermine an initial position of the movable conductive layer withrespect to at least one of the one or more fixed conductive layers, anda controller configured to determine a charging voltage based at leastin part on the initial position, and apply the charging voltage to themovable conductive layer.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a method of positioning a movableconductive layer that is movable with respect to one or more fixedconductive layers in a display. The method includes determining aninitial position of the movable conductive layer with respect to atleast one of the one or more fixed conductive layers, determining acharging voltage based at least in part on the initial position, andapplying the charging voltage to the movable conductive layer.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for driving a displayincluding a movable conductive layer and one or more fixed conductivelayers. The apparatus includes means for determining an initial positionof the movable conductive layer with respect to at least one of the oneor more fixed conductive layers, means for determining a chargingvoltage based at least in part on the initial position, and means forapplying the charging voltage to the movable conductive layer.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a computer program product forpositioning a movable conductive layer that is movable with respect toone or more fixed conductive layers in a display. The computer programproduct includes a non-transitory computer-readable medium having storedthereon code for causing processing circuitry to determine an initialposition of the movable conductive layer with respect to at least one ofthe one or more fixed conductive layers, determine a charging voltagebased at least in part on the initial position, and apply the chargingvoltage to the movable conductive layer.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show examples of isometric views depicting a pixel of aninterferometric modulator (IMOD) display device in two different states.

FIG. 2 shows an example of a schematic circuit diagram illustrating adriving circuit array for an optical MEMS display device.

FIG. 3 is an example of a schematic partial cross-section illustratingone implementation of the structure of the driving circuit and theassociated display element of FIG. 2.

FIG. 4 is an example of a schematic exploded partial perspective view ofan optical MEMS display device having an interferometric modulator arrayand a backplate with embedded circuitry.

FIG. 5 is a cross-section of an implementation of an interferometricmodulator having two fixed layers and a movable third layer.

FIG. 6 shows an example of a schematic circuit diagram illustrating adriving circuit array for a display device having the structure of FIG.5.

FIG. 7 is a schematic representation of the interferometric modulatorand voltage sources illustrated in FIG. 5.

FIG. 8 illustrates a portion of a display array driving circuitaccording to some implementations.

FIG. 9 illustrates a flowchart of a method for controlling the positionof a movable conductive layer according to some implementations.

FIG. 10 illustrates a portion of a display array driving and positionsensing circuit according to some implementations.

FIG. 11 illustrates an example of a method of sequential adjustment of amovable third layer 806 according to some implementations.

FIG. 12 illustrates a portion of a display array driving and sensingcircuit including circuitry for testing pixel characteristics.

FIG. 13 is a flowchart of a method of determining the launch conditionΔx_(L), according to some implementations.

FIG. 14 is a flowchart of a method of determining the spring stiffness Kaccording to some implementations.

FIG. 15 is a flowchart of a calibrated adjustment method according tosome implementations.

FIG. 16 illustrates an example of a circuit configured to generate apulsed voltage signal for inducing charge to the movable third layer806.

FIG. 17 illustrates another example of a circuit configured to generatea pulsed voltage signal for inducing charge to the movable third layer806.

FIGS. 18A and 18B show examples of system block diagrams illustrating adisplay device that includes a plurality of interferometric modulators.

FIG. 19 is an example of a schematic exploded perspective view of anelectronic device having an optical MEMS display.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following detailed description is directed to certainimplementations for the purposes of describing the innovative aspects.However, the teachings herein can be applied in a multitude of differentways. The described implementations may be implemented in any devicethat is configured to display an image, whether in motion (such asvideo) or stationary (such as still image), and whether textual,graphical or pictorial. More particularly, it is contemplated that theimplementations may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,multimedia Internet enabled cellular telephones, mobile televisionreceivers, wireless devices, smartphones, bluetooth devices, personaldata assistants (PDAs), wireless electronic mail receivers, hand-held orportable computers, netbooks, notebooks, smartbooks, printers, copiers,scanners, facsimile devices, GPS receivers/navigators, cameras, MP3players, camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, electronic reading devices(such as e-readers), computer monitors, auto displays (such as odometerdisplay, etc.), cockpit controls and/or displays, camera view displays(such as display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures, microwaves, refrigerators, stereo systems, cassetterecorders or players, DVD players, CD players, VCRs, radios, portablememory chips, washers, dryers, washer/dryers, parking meters, packaging(such as MEMS and non-MEMS), aesthetic structures (such as display ofimages on a piece of jewelry) and a variety of electromechanical systemsdevices. The teachings herein also can be used in non-displayapplications such as, but not limited to, electronic switching devices,radio frequency filters, sensors, accelerometers, gyroscopes,motion-sensing devices, magnetometers, inertial components for consumerelectronics, parts of consumer electronics products, varactors, liquidcrystal devices, electrophoretic devices, drive schemes, manufacturingprocesses, and electronic test equipment. Thus, the teachings are notintended to be limited to the implementations depicted solely in theFigures, but instead have wide applicability as will be readily apparentto a person having ordinary skill in the art.

Certain methods and devices described herein relate to implementationsof analog interferometric modulators. An analog interferometricmodulator may be driven to a range of different positions to generate avariable optical response. The optical response of the analoginterferometric modulator is a function of the charge present at amovable electrode, and the corresponding position of the movableelectrode relative to the other electrodes of the analog interferometricmodulator. Methods and systems for calibrating and controlling theposition of an analog interferometric modulator to achieve variousoptical responses are disclosed.

According to some implementations, methods and systems for controllingthe position of movable electrode relative to stationary electrodes ofan analog display element are disclosed. Particular implementations ofthe subject matter described in this disclosure can be implemented todetermine an amount of charge to be applied to a movable electrode toreach a desired position. The positional response of a movable electrodedepends not only on the voltage being applied, but also the particularelectrode position prior to application of the voltage. The disclosedsystems and method may include accurate determination of a charge to beapplied based at lest in part on the current position of the movableelectrode and the final desired position of the movable electrode.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. The systems and methods disclosed herein can allowfast and accurate positioning of a movable electrode in an analoginterferometric modulator. Further, the systems and methods disclosedherein can increase the ability to produce a high performance array ofmodulators in a display device even when the physical properties of themodulators of the array include different response characteristics due,for example, to fabrication tolerances. Further, the use of a sequentialdrive-and-update scheme as will be described according to someimplementations below may advantageously be used to drive modulatorshaving a slower response time than modulators than are driven using acontinuous feedback driving scheme.

According to some implementations, method and systems for driving ananalog display element (such as an IMOD having three or more states)efficiently are disclosed, such that superior brightness and highercolor gamut may be achieved relative to a display including binarydisplay elements. Further, a display including analog display elements(such as IMODs) allows each pixel of the display to be configured as anyone of red, green, or blue pixels, thereby reducing and/or eliminatingthe need for sub-pixel arrays for generating different colors. As aresult, the spatial resolution of a display including analog displayelements (such as IMODs) display can be improved relative to a displayhaving binary display elements. Further, tone scale resolution may alsobe improved for a display including analog display elements relative toa display having binary display elements.

An example of a suitable MEMS device, to which the describedimplementations may apply, is a reflective display device. Reflectivedisplay devices can incorporate interferometric modulators (IMODs) toselectively absorb and/or reflect light incident thereon usingprinciples of optical interference. IMODs can include an absorber, areflector that is movable with respect to the absorber, and an opticalresonant cavity defined between the absorber and the reflector. Thereflector can be moved to two or more different positions, which canchange the size of the optical resonant cavity and thereby affect thereflectance of the interferometric modulator. The reflectance spectrumsof IMODs can create fairly broad spectral bands which can be shiftedacross the visible wavelengths to generate different colors. Theposition of the spectral band can be adjusted by changing the thicknessof the optical resonant cavity, i.e., by changing the position of thereflector.

FIGS. 1A and 1B show examples of isometric views depicting a pixel of aninterferometric modulator (IMOD) display device in two different states.The IMOD display device includes one or more interferometric MEMSdisplay elements. In these devices, the pixels of the MEMS displayelements can be in either a bright or dark state. In the bright(“relaxed,” “open” or “on”) state, the display element reflects a largeportion of incident visible light, such as to a user. Conversely, in thedark (“actuated,” “closed” or “off”) state, the display element reflectslittle incident visible light. In some implementations, the lightreflectance properties of the on and off states may be reversed. MEMSpixels can be configured to reflect predominantly at particularwavelengths allowing for a color display in addition to black and white.In the example illustrated in FIGS. 1A and 1B, a binary or two-statedisplay element is illustrated. An analog display element (such as adisplay element having three or more states) will be described ingreater below with reference to FIG. 5.

The IMOD display device can include a row/column array of IMODs. EachIMOD can include a pair of reflective layers, i.e., a movable reflectivelayer and a fixed partially reflective layer, positioned at a variableand controllable distance from each other to form an air gap (alsoreferred to as an optical gap or cavity). The movable reflective layermay be moved between at least two positions. In a first position, i.e.,a relaxed position, the movable reflective layer can be positioned at arelatively large distance from the fixed partially reflective layer. Ina second position, i.e., an actuated position, the movable reflectivelayer can be positioned more closely to the partially reflective layer.Incident light that reflects from the two layers can interfereconstructively or destructively depending on the position of the movablereflective layer, producing either an overall reflective ornon-reflective state for each pixel. In some implementations, the IMODmay be in a reflective state when unactuated, reflecting light withinthe visible spectrum, and may be in a dark state when unactuated,reflecting light outside of the visible range (such as infrared light).In some other implementations, however, an IMOD may be in a dark statewhen unactuated, and in a reflective state when actuated. In someimplementations, the introduction of an applied voltage can drive thepixels to change states. In some other implementations, an appliedcharge can drive the pixels to change states.

The depicted pixels in FIGS. 1A and 1B depict two different states of anIMOD 12. In the IMOD 12 in FIG. 1A, a movable reflective layer 14 isillustrated in a relaxed position at a predetermined (such as, designed)distance from an optical stack 16, which includes a partially reflectivelayer. Since no voltage is applied across the IMOD 12 in FIG. 1A, themovable reflective layer 14 remained in a relaxed or unactuated state.In the IMOD 12 in FIG. 1B, the movable reflective layer 14 isillustrated in an actuated position and adjacent, or nearly adjacent, tothe optical stack 16. The voltage V_(actuate) applied across the IMOD 12in FIG. 1B is sufficient to actuate the movable reflective layer 14 toan actuated position.

In FIGS. 1A and 1B, the reflective properties of pixels 12 are generallyillustrated with arrows 13 indicating light incident upon the pixels 12,and light 15 reflecting from the pixel 12 on the left. Although notillustrated in detail, it will be understood by a person having ordinaryskill in the art that most of the light 13 incident upon the pixels 12will be transmitted through the transparent substrate 20, toward theoptical stack 16. A portion of the light incident upon the optical stack16 will be transmitted through the partially reflective layer of theoptical stack 16, and a portion will be reflected back through thetransparent substrate 20. The portion of light 13 that is transmittedthrough the optical stack 16 will be reflected at the movable reflectivelayer 14, back toward (and through) the transparent substrate 20.Interference (constructive or destructive) between the light reflectedfrom the partially reflective layer of the optical stack 16 and thelight reflected from the movable reflective layer 14 will determine thewavelength(s) of light 15 reflected from the pixels 12.

The optical stack 16 can include a single layer or several layers. Thelayer(s) can include one or more of an electrode layer, a partiallyreflective and partially transmissive layer and a transparent dielectriclayer. In some implementations, the optical stack 16 is electricallyconductive, partially transparent and partially reflective, and may befabricated, for example, by depositing one or more of the above layersonto a transparent substrate 20. The electrode layer can be formed froma variety of materials, such as various metals, for example indium tinoxide (ITO). The partially reflective layer can be formed from a varietyof materials that are partially reflective, such as various metals,e.g., chromium (Cr), semiconductors, and dielectrics. The partiallyreflective layer can be formed of one or more layers of materials, andeach of the layers can be formed of a single material or a combinationof materials. In some implementations, the optical stack 16 can includea single semi-transparent thickness of metal or semiconductor whichserves as both an optical absorber and conductor, while different, moreconductive layers or portions (such as of the optical stack 16 or ofother structures of the IMOD) can serve to bus signals between IMODpixels. The optical stack 16 also can include one or more insulating ordielectric layers covering one or more conductive layers or aconductive/absorptive layer.

In some implementations, the optical stack 16, or lower electrode, isgrounded at each pixel. In some implementations, this may beaccomplished by depositing a continuous optical stack 16 onto thesubstrate 20 and grounding at least a portion of the continuous opticalstack 16 at the periphery of the deposited layers. In someimplementations, a highly conductive and reflective material, such asaluminum (Al), may be used for the movable reflective layer 14. Themovable reflective layer 14 may be formed as a metal layer or layersdeposited on top of posts 18 and an intervening sacrificial materialdeposited between the posts 18. When the sacrificial material is etchedaway, a defined gap 19, or optical cavity, can be formed between themovable reflective layer 14 and the optical stack 16. In someimplementations, the spacing between posts 18 may be on the order of1-1,000 um, while the gap 19 may be on the order of <10,000 Angstroms(Å).

In some implementations, each pixel of the IMOD, whether in the actuatedor relaxed state, is essentially a capacitor formed by the fixed andmoving reflective layers. When no voltage is applied, the movablereflective layer 14 a remains in a mechanically relaxed state, asillustrated by the pixel 12 in FIG. 1A, with the gap 19 between themovable reflective layer 14 and optical stack 16. However, when apotential difference, such as a voltage, is applied to at least one ofthe movable reflective layer 14 and optical stack 16, the capacitorformed at the corresponding pixel becomes charged, and electrostaticforces pull the electrodes together. If the applied voltage exceeds athreshold, the movable reflective layer 14 can deform and move near oragainst the optical stack 16. A dielectric layer (not shown) within theoptical stack 16 may prevent shorting and control the separationdistance between the layers 14 and 16, as illustrated by the actuatedpixel 12 in FIG. 1B. The behavior is the same regardless of the polarityof the applied potential difference. Though a series of pixels in anarray may be referred to in some instances as “rows” or “columns,” aperson having ordinary skill in the art will readily understand thatreferring to one direction as a “row” and another as a “column” isarbitrary. Restated, in some orientations, the rows can be consideredcolumns, and the columns considered to be rows. Furthermore, the displayelements may be evenly arranged in orthogonal rows and columns (an“array”), or arranged in non-linear configurations, for example, havingcertain positional offsets with respect to one another (a “mosaic”). Theterms “array” and “mosaic” may refer to either configuration. Thus,although the display is referred to as including an “array” or “mosaic,”the elements themselves need not be arranged orthogonally to oneanother, or disposed in an even distribution, in any instance, but mayinclude arrangements having asymmetric shapes and unevenly distributedelements.

In some implementations, such as in a series or array of IMODs, theoptical stacks 16 can serve as a common electrode that provides a commonvoltage to one side of the IMODs 12. The movable reflective layers 14may be formed as an array of separate plates arranged in, for example, amatrix form. The separate plates can be supplied with voltage signalsfor driving the IMODs 12.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, the movable reflective layers 14 of each IMOD 12 may beattached to supports at the corners only, such as on tethers. As shownin FIG. 3, a flat, relatively rigid movable reflective layer 14 may besuspended from a deformable layer 34, which may be formed from aflexible metal. This architecture allows the structural design andmaterials used for the electromechanical aspects and the optical aspectsof the modulator to be selected, and to function, independently of eachother. Thus, the structural design and materials used for the movablereflective layer 14 can be optimized with respect to the opticalproperties, and the structural design and materials used for thedeformable layer 34 can be optimized with respect to desired mechanicalproperties. For example, the movable reflective layer 14 portion may bealuminum, and the deformable layer 34 portion may be nickel. Thedeformable layer 34 may connect, directly or indirectly, to thesubstrate 20 around the perimeter of the deformable layer 34. Theseconnections may form the support posts 18.

In implementations such as those shown in FIGS. 1A and 1B, the IMODsfunction as direct-view devices, in which images are viewed from thefront side of the transparent substrate 20, i.e., the side opposite tothat upon which the modulator is arranged. In these implementations, theback portions of the device (that is, any portion of the display devicebehind the movable reflective layer 14, including, for example, thedeformable layer 34 illustrated in FIG. 3) can be configured andoperated upon without impacting or negatively affecting the imagequality of the display device, because the reflective layer 14 opticallyshields those portions of the device. For example, in someimplementations a bus structure (not illustrated) can be included behindthe movable reflective layer 14 which provides the ability to separatethe optical properties of the modulator from the electromechanicalproperties of the modulator, such as voltage addressing and themovements that result from such addressing.

FIG. 2 shows an example of a schematic circuit diagram illustrating adriving circuit array 200 for an optical MEMS display device. Thedriving circuit array 200 can be used for implementing an active matrixaddressing scheme for providing image data to display elementsD₁₁-D_(mn) of a display array assembly.

The driving circuit array 200 includes a data driver 210, a gate driver220, first to m-th data lines DL1-DLm, first to n-th gate lines GL1-GLn,and an array of switches or switching circuits S₁₁-S_(mn). Each of thedata lines DL1-DLm extends from the data driver 210, and is electricallyconnected to a respective column of switches S₁₁-S_(1n), S₂₁-S_(2n),S_(m1)-S_(mn). Each of the gate lines GL1-GLn extends from the gatedriver 220, and is electrically connected to a respective row ofswitches S₁₁-S_(m1), S₁₂-S_(m2), S_(1n)-S_(mn). The switches S₁₁-S_(mn)are electrically coupled between one of the data lines DL1-DLm and arespective one of the display elements D₁₁-D_(mn) and receive aswitching control signal from the gate driver 220 via one of the gatelines GL1-GLn. The switches S₁₁-S_(mn) are illustrated as single FETtransistors, but may take a variety of forms such as two transistortransmission gates (for current flow in both directions) or evenmechanical MEMS switches.

The data driver 210 can receive image data from outside the display, andcan provide the image data on a row by row basis in a form of voltagesignals to the switches S₁₁-S_(mn) via the data lines DL1-DLm. The gatedriver 220 can select a particular row of display elements D₁₁-D_(m1),D₁₂-D_(m2), . . . , D_(1n)-D_(mn) by turning on the switches S₁₁-S_(m1),S₁₂-S_(m2), . . . , S_(1n)-S_(mn) associated with the selected row ofdisplay elements D₁₁-D_(m1), D₁₂-D_(m2), . . . , D_(1n)-D_(mn). When theswitches S₁₁-S_(m1), S₁₂-S_(m2), . . . , S_(1n)-S_(mn) in the selectedrow are turned on, the image data from the data driver 210 is passed tothe selected row of display elements D₁₁-D_(m1), D₁₂-D_(m2), . . . ,D_(1n)-D_(mn).

During operation, the gate driver 220 can provide a voltage signal viaone of the gate lines GL1-GLn to the gates of the switches S₁₁-S_(mn) ina selected row, thereby turning on the switches S₁₁-S_(mn). After thedata driver 210 provides image data to all of the data lines DL1-DLm,the switches S₁₁S_(mn) of the selected row can be turned on to providethe image data to the selected row of display elements D₁₁-D_(m1),D₁₂-D_(m2), . . . , D_(1n)-D_(mn), thereby displaying a portion of animage. For example, data lines DL that are associated with pixels thatare to be actuated in the row can be set to, a voltage, such as 10-volts(could be positive or negative), and data lines DL that are associatedwith pixels that are to be released in the row can be set to, a voltage,such as O-volts. Then, the gate line GL for the given row is asserted,turning the switches in that row on, and applying the selected data linevoltage to each pixel of that row. This charges and actuates the pixelsthat have 10-volts applied, and discharges and releases the pixels thathave O-volts applied. Then, the switches S₁₁-S_(mn) can be turned off.The display elements D₁₁-D_(m1), D₁₂-D_(m2), . . . , D₁-D_(mn) can holdthe image data because the charge on the actuated pixels will beretained when the switches are off, except for some leakage throughinsulators and the off state switch. Generally, this leakage is lowenough to retain the image data on the pixels until another set of datais written to the row. These steps can be repeated to each succeedingrow until all of the rows have been selected and image data has beenprovided thereto. In the implementation of FIG. 2, the optical stack 16is grounded at each pixel. In some implementations, this may beaccomplished by depositing a continuous optical stack 16 onto thesubstrate and grounding the entire sheet at the periphery of thedeposited layers.

FIG. 3 is an example of a schematic partial cross-section illustratingone implementation of the structure of the driving circuit and theassociated display element of FIG. 2. A portion 201 of the drivingcircuit array 200 includes the switch S₂₂ at the second column and thesecond row, and the associated display element D₂₂. In the illustratedimplementation, the switch S₂₂ includes a transistor 80. Other switchesin the driving circuit array 200 can have the same configuration as theswitch S₂₂, or can be configured differently, for example by changingthe structure, the polarity, or the material.

FIG. 3 also includes a portion of a display array assembly 110, and aportion of a backplate 120. The portion of the display array assembly110 includes the display element D₂₂ of FIG. 2. The display element D₂₂includes a portion of a front substrate 20, a portion of an opticalstack 16 formed on the front substrate 20, supports 18 formed on theoptical stack 16, a movable reflective layer 14 (or a movable electrodeconnected to a deformable layer 34) supported by the supports 18, and aninterconnect 126 electrically connecting the movable reflective layer 14to one or more components of the backplate 120.

The portion of the backplate 120 includes the second data line DL2 andthe switch S₂₂ of FIG. 2, which are embedded in the backplate 120. Theportion of the backplate 120 also includes a first interconnect 128 anda second interconnect 124 at least partially embedded therein. Thesecond data line DL2 extends substantially horizontally through thebackplate 120. The switch S₂₂ includes a transistor 80 that has a source82, a drain 84, a channel 86 between the source 82 and the drain 84, anda gate 88 overlying the channel 86. The transistor 80 can be, e.g., athin film transistor (TFT) or metal-oxide-semiconductor field effecttransistor (MOSFET). The gate of the transistor 80 can be formed by gateline GL2 extending through the backplate 120 perpendicular to data lineDL2. The first interconnect 128 electrically couples the second dataline DL2 to the source 82 of the transistor 80.

The transistor 80 is coupled to the display element D₂₂ through one ormore vias 160 through the backplate 120. The vias 160 are filled withconductive material to provide electrical connection between components(for example, the display element D₂₂) of the display array assembly 110and components of the backplate 120. In the illustrated implementation,the second interconnect 124 is formed through the via 160, andelectrically couples the drain 84 of the transistor 80 to the displayarray assembly 110. The backplate 120 also can include one or moreinsulating layers 129 that electrically insulate the foregoingcomponents of the driving circuit array 200.

The optical stack 16 of FIG. 3 is illustrated as three layers, a topdielectric layer described above, a middle partially reflective layer(such as chromium) also described above, and a lower layer including atransparent conductor (such as indium-tin-oxide (ITO)). The commonelectrode is formed by the ITO layer and can be coupled to ground at theperiphery of the display. In some implementations, the optical stack 16can include more or fewer layers. For example, in some implementations,the optical stack 16 can include one or more insulating or dielectriclayers covering one or more conductive layers or a combinedconductive/absorptive layer.

FIG. 4 is an example of a schematic exploded partial perspective view ofan optical MEMS display device 30 having an interferometric modulatorarray and a backplate with embedded circuitry. The display device 30includes a display array assembly 110 and a backplate 120. In someimplementations, the display array assembly 110 and the backplate 120can be separately pre-formed before being attached together. In someother implementations, the display device 30 can be fabricated in anysuitable manner, such as, by forming components of the backplate 120over the display array assembly 110 by deposition.

The display array assembly 110 can include a front substrate 20, anoptical stack 16, supports 18, a movable reflective layer 14, andinterconnects 126. The backplate 120 can include backplate components122 at least partially embedded therein, and one or more backplateinterconnects 124.

The optical stack 16 of the display array assembly 110 can be asubstantially continuous layer covering at least the array region of thefront substrate 20. The optical stack 16 can include a substantiallytransparent conductive layer that is electrically connected to ground.The reflective layers 14 can be separate from one another and can have,a shape, such as, a square or rectangular shape. The movable reflectivelayers 14 can be arranged in a matrix form such that each of the movablereflective layers 14 can form part of a display element. In theimplementation illustrated in FIG. 4, the movable reflective layers 14are supported by the supports 18 at four corners.

Each of the interconnects 126 of the display array assembly 110 servesto electrically couple a respective one of the movable reflective layers14 to one or more backplate components 122 (such as transistors S and/orother circuit elements). In the illustrated implementation, theinterconnects 126 of the display array assembly 110 extend from themovable reflective layers 14, and are positioned to contact thebackplate interconnects 124. In another implementation, theinterconnects 126 of the display array assembly 110 can be at leastpartially embedded in the supports 18 while being exposed through topsurfaces of the supports 18. In such an implementation, the backplateinterconnects 124 can be positioned to contact exposed portions of theinterconnects 126 of the display array assembly 110. In yet anotherimplementation, the backplate interconnects 124 can extend from thebackplate 120 toward the movable reflective layers 14 so as to contactand thereby electrically connect to the movable reflective layers 14.

The interferometric modulators described above have been described asbi-stable elements having a relaxed state and an actuated state. Theabove and following description, however, also may be used with analoginterferometric modulators having a range of states. For example, ananalog interferometric modulator can have a red state, a green state, ablue state, a black state and a white state, in addition to other colorstates. In some implementations, a display element (such as an analogIMOD illustrated in FIG. 5 described further below) has 3, 4, 7, 8, 15,16, 31, 32, 63, 64, 127, 128, 255, or 256 states. In someimplementations, the states may not be quantized, and an essentiallycontinuously variable state may be achieved. Accordingly, a singleinterferometric modulator can be configured to have various states withdifferent light reflectance properties over a wide range of the opticalspectrum.

FIG. 5 is a cross-section of an implementation of an interferometricmodulator having two fixed layers and a movable third layer. Asillustrated, the interferometric modulator of FIG. 5 is illustrated tobe viewed from the side of a substrate 820. FIG. 5 shows animplementation of an analog interferometric modulator having a fixedfirst layer 802, a fixed second layer 804, and a movable third layer 806positioned between the fixed first and second layers 802 and 804. Eachof the layers 802, 804, and 806 may include an electrode or otherconductive material. For example, the fixed first layer 802 may includea layer made of metal. The fixed first layer 802 and fixed second layer804 may be referred to herein as fixed conductive layers, while themovable third layer 806 may be referred to herein as a movableconductive layer. Each of the layers 802, 804, and 806 may be stiffenedusing a stiffening layer formed on or deposited on the respective layer.In one implementation, the stiffening layer includes a dielectric. Thestiffening layer may be used to keep the layer to which it is attachedrigid and substantially flat. Some implementations of theinterferometric modulator may be referred to as a three-terminalinterferometric modulator.

Certain of the implementations described herein may be implemented byomitting one of the electrodes (such as fixed first layer 802 or fixedsecond layer 804). In these implementations, a voltage V_(m) may beapplied to a movable layer that has a variable position relative to asingle layer coupled to ground. In this way, an analog modulator havingtwo terminals rather than three can be formed, and the methods describedherein may be applied to such two-terminal modulators.

The three layers 802, 804, and 806 are electrically insulated byinsulating posts 810. The movable third layer 806 is suspended from theinsulating posts 810. The movable third layer 806 is configured todeform such that the movable third layer 806 may be displaced towardsthe substrate 820, and as illustrated in FIG. 5, toward the fixed firstlayer 802, or may be displaced in away from the substrate 820, and asillustrated in FIG. 5, toward the fixed second layer 804. In someimplementations, the fixed first layer 802 may also refer to theelectrode layer closer to the substrate 820, while the fixed secondlayer 804 may refer to the electrode layer farther from the substrate820

In FIG. 5, the movable third layer 806 is illustrated as being in anequilibrium position with the solid lines. As illustrated, d₁corresponds to the nominal distance between the fixed second layer 804and the movable third layer 806, while d₂ corresponds to the nominaldistance between the fixed first layer 802 and the movable third layer806. The position of the movable third layer 806 from the middleposition between the fixed first layer 802 and fixed second layer 806(such as the position at which d₁=d₂) may be indicated by a value x asillustrated in FIG. 5, where a positive value of x corresponds to aposition closer to the fixed first layer 802 and a negative value of xcorresponds to a distance that is farther from the fixed first layer802. When positioned at a substantial midpoint (such as the position atwhich d₁=d₂) between the fixed first layer 802 and the fixed secondlayer 804, the position of the movable third layer 806 may correspond toa nominal position X₀.

As illustrated in FIG. 5, a fixed voltage difference may be appliedbetween the fixed first layer 802 and the fixed second layer 804. In theimplementation of FIG. 5, a voltage V₀ is applied to fixed first layer802 while fixed second layer 804 is grounded. A person/one havingordinary skill in the art will recognize that the alternativearrangement is also possible (such as when a voltage V₀ is applied tothe fixed second layer 804 and the fixed first layer 802 is grounded).If a variable voltage V_(m) is applied to the movable third layer 806,then as that voltage V_(m) approaches V₀, the movable third layer 806will be electrostatically pulled toward fixed second layer 804. As thatvoltage V_(m) approaches ground, the movable third layer 806 will beelectrostatically pulled toward fixed first layer 802. Ideally, if avoltage at the midpoint of these two voltages (V₀/2 in thisimplementation) is applied to movable third layer 806, then the movablethird layer 806 will be maintained in its equilibrium position indicatedwith solid lines in FIG. 5. By applying a variable voltage to themovable third layer 806 that is between the voltages on fixed first andsecond layers 802 and 804, the movable third layer 806 can be positionedat a desired location between fixed first and second layers 802 and 804,producing a desired optical response. This desired position may bereferred herein as a desired position or final position x_(F). Asillustrated in FIG. 5, the position of movable third layer 806 relativeto the fixed first layer 802 and fixed second layer 804 corresponds toplural states for the display element 800 such that each state has adifferent optical response.

The voltage difference V₀ between the fixed first and second layers 802and 804 can vary widely depending on the materials and construction ofthe device, and in many implementations may be in the range of about5-20 volts. As the movable third layer 806 moves away from theequilibrium position (X₀), it will deform or bend. In such deformed orbent configuration, an elastic spring force mechanically biases themovable third layer 806 toward the equilibrium position. This mechanicalforce (which may be referred to as a spring stiffness K) alsocontributes to the final position of the movable third layer 806 when avoltage V_(m) is applied thereto.

The movable third layer 806 may include a mirror to reflect lightentering the interferometric modulator through substrate 820. The mirrormay include a metal material. The fixed second layer 804 may include apartially absorbing material such that the fixed second layer 804 actsas an absorbing layer. This absorbing material may be as described abovewith reference to the optical stack 16 illustrated in FIG. 1. When lightreflected from the movable third layer 806 is viewed from the side ofthe substrate 820 opposing movable third layer 806, the viewer mayperceive the reflected light as a certain color. By adjusting theposition of the movable third layer 806, certain wavelengths of lightmay be selectively reflected.

FIG. 6 shows an example of a schematic circuit diagram illustrating adriving circuit array for a display device having the structure of FIG.5. The overall apparatus shares many similarities to the structure ofFIG. 2 that uses the bi-stable interferometric modulators. As shown inFIG. 6, however, an additional layer, corresponding to fixed first layer802 is provided for each display element. The fixed first layer 802 maybe deposited on the inside surface of the backplate 120 facing themovable layer shown in FIGS. 3 and 4, and may have a voltage V₀ appliedthereto as described with reference to FIG. 5. The data driver 210 andgate driver 220 of FIG. 6 can be used in a manner similar to thatdescribed above with reference to FIG. 2, except the voltages providedon the data lines DL1-DLn can be placed at a range of voltages betweenV₀ and ground, rather than at one of only two different voltages. Inthis way, the movable third layers 806 of the display elements along arow can each be independently placed in any particular desired positionbetween the fixed first layer 802 and the fixed second layer 804 whenthe row is written by asserting the gate line for that particular row.

FIG. 7 is a schematic representation of the interferometric modulatorand voltage sources illustrated in FIG. 5. In this schematic, themodulator is coupled to the voltage sources V₀ and V_(m). The equivalentcircuit model of the interferrometric modulator and voltage sources isshown in FIG. 7. Each interferometric modulator pixel is selectivelyconnected to a data line (such as DL1-DLn) by a switch S1. Each dataline may include an associated parasitic capacitance, illustrated ascapacitance C_(P). As illustrated, each interferometric modulator alsoincludes associated parasitic capacitances C_(P1) and C_(P2), which aretypically small. The gap between the fixed first layer 802 and themovable third layer 806 may correspond to a variable capacitance C₂(x),while the gap between the movable third layer 806 and the fixed secondlayer 804 may correspond to a variable capacitance C₁(x). Thecapacitance values C₁(x) and C₂(x) are each a function of the position(x) of the movable third layer 806. Thus, in the schematicrepresentation illustrated in FIG. 7, the voltage source V₀ is connectedacross the coupled capacitors C_(P1), C_(P2), C₁(x), and C₂(x) while thevoltage source V_(m) is connected to the middle layer 806 between theparallel coupled capacitors C_(P1), C₁(x), and the parallel coupledcapacitors C_(P2), C₂(x).

Accurately driving the movable third layer 806 to different positionsusing the voltage sources V₀ and V_(m) as described above, however, maybe difficult with many configurations of the interferometric modulatorbecause the relationship between voltage applied to the modulator andthe position of the movable third layer 806 may be highly non-linear.Further, applying the same voltage V_(m) to the movable third layers 806of different interferometric modulators may not cause the respectivemovable third layers 806 to move to the same position relative to thefixed first layer 802 and fixed second layer 804 of each modulator dueto manufacturing differences, for example, variations in thickness orelasticity of the movable third layers 806 over the entire displaysurface. As the position of the movable third layer 806 will determinewhat color is reflected from the interferometric modulator, as discussedabove, accurately driving the movable third layer 806 to desiredpositions allows more accurate control of a displayed image. In manyimplementations described in more detail below, through operation of theswitch S₁, an isolated charge (Q_(m)) may be applied to the movablethird layer 806 in order to move the movable third layer 806 to thedesired position.

During operation of a display in accordance with some implementations, agiven pixel may be placed at a series of desired positions in accordancewith a series of frames of image data by successively placing andisolating a series of isolated charges Q on the pixel in accordance withthe corresponding series of desired positions. The magnitude of thedisplacement from central undeflected position X₀ will be denoted hereinby the variable “x”. Initial and final values for this variable x may bereferred to as x₀ and x₁ respectively. As described in additional detailbelow, the position of the display element may be adjusted bydetermining the desired charge Q_(m) required for placing the layer 806at new desired position x₁. Then, the voltage necessary to place thischarge on the middle layer 806 when the layer 806 is in its currentposition x₀ is determined (the initial position x₀ may, and often will,be different from the no displacement central position X₀ describedabove with reference to FIG. 5). This voltage is applied to the middlelayer when it is in position x₀, the new charge state is then isolatedon the middle layer 806, and the middle layer 806 then moves to the newposition x₁. Since the mechanical response of the movable third layer806 to an applied voltage may be slow relative to the time necessary toplace a desired charge on the third layer 806, during the very shorttime interval when the switch 51 is closed, the mirror position may notchange significantly.

The amount of charge to place on the mirror 806 may be based on modelingthe response of the interferrometric modulator which will be describedin greater detail with reference to Equation 1 below. The steady stateposition of the mirror may be described by Equation 1 which balanceselectrostatic forces on the mirror 806 with a restoring spring force:

$\begin{matrix}{{{\frac{Q_{m}^{2}}{2ɛ_{0}A_{P}}( \frac{d_{1} - d_{2} + {2x}}{d_{1} + d_{2}} )} - \frac{Q_{m}V_{0}}{d_{1} + d_{2}} - {K( {x - {\Delta\; x_{L}}} )}} = 0} & (1)\end{matrix}$

In this formula, K is the spring stiffness value, A_(P) is the area ofthe movable third layer 806 (such as the mirror) electrode, V₀ is thestatic bias applied between the fixed first layer 802 and the fixedsecond layer 804, Q_(m) is the isolated charge on the movable thirdlayer 806, d₁ corresponds to the distance between the fixed second layer804 and the movable third layer 806 under no deformation from itsnominal position, d₂ corresponds to the distance between the fixed firstlayer 802 and the movable third layer 806 under no deformation from itsnominal position, ∈₀ is the permittivity constant, and Δx_(L), is the“launch condition” of the movable third layer 806. The launch conditionof the movable third layer 806 as referred to herein corresponds toposition where the movable third layer 806 rests when there is noelectrostatic force acting on it (for example, when all three layers802, 804, and 806 are at the same potential), due to, for example,fabrication induced mechanical bias, or the like.

Solving Equation 1 above for the charge Q_(m) as a function of x resultsin Equation 2 below:

$\begin{matrix}{{Q_{m}(x)} = {\frac{ɛ_{0}A_{P}V_{0}}{d_{1} - d_{2} + {2x}}\{ {1 - \sqrt{1 + {\frac{2K}{ɛ_{0}A_{P}V_{0}^{2}}( {d_{1} + d_{2}} )( {d_{1} - d_{2} + {2x}} )( {x - {\Delta\; x_{L}}} )}}} \}}} & (2)\end{matrix}$

Expansion of the square root by Taylor's series shows that the leadingterm is linear with the position x and varies inversely with (V₀(d₁+d₂))as represented in Equation 3 below.

$\begin{matrix}{{Q_{m}(x)} = {{\frac{ɛ_{0}A_{P}V_{0}}{d_{1} - d_{2} + {2x}}\{ {1 - ( {1 + {\frac{K}{ɛ_{0}A_{P}V_{0}^{2}}( {d_{1} + d_{2}} )( {d_{1} - d_{2} + {2x}} )( {x - {\Delta\; x_{L}}} )} + \ldots}\mspace{14mu} )} \}} \approx {\frac{{- {K( {x - {\Delta\; x_{L}}} )}}( {d_{1} + d_{2}} )}{V_{0}} + \ldots}}} & (3)\end{matrix}$

The negative value in this formula is due to the choice of geometry. Forexample, in FIG. 5 above, a positive voltage on the fixed first layer802 sets up an electric field that is directed in the negative xdirection.

The value of the voltage V_(m) needed to produce a net charge of Q_(m)on the mirror when the mirror is at the position x=x₀ is given byEquation 4 below:

$\begin{matrix}{V_{m} = {\frac{( {{C_{2}( x_{0} )} + C_{P\; 2}} )V_{0}}{{C_{1}( x_{0} )} + {C_{2}( x_{0} )} + C_{P\; 1} + C_{P\; 2}} + {( \frac{1}{{C_{1}( x_{0} )} + {C_{2}( x_{0} )}} )Q_{m}}}} & (4)\end{matrix}$where Q_(m) is the charge needed to move the mirror to a desiredposition x₁ so that the voltage needed to do the same is a function oftwo position variables, the current position x₀ and the next positionx₁. The values of the variable capacitance associated with the movablethird layer 806 are given by Equation 5:

$\begin{matrix}{{{C_{1}( x_{0} )} = \frac{ɛ_{0}A_{P}}{d_{1} + x_{0}}},{{C_{2}( x_{0} )} = \frac{ɛ_{0}A_{P}}{d_{2} - x_{0}}}} & (5)\end{matrix}$

After the movable third layer 806 is charged, the movable third layer806 moves and settles at the new position x₁, at which point the voltageon the movable third layer is given by Equation 6:

$\begin{matrix}{{V_{C}(\infty)} = {\frac{( {{C_{2}( x_{1} )} + C_{P\; 2}} )V_{0}}{{C_{1}( x_{1} )} + {C_{2}( x_{1} )} + C_{P\; 1} + C_{P\; 2}} + {( \frac{1}{{C_{1}( x_{1} )} + {C_{2}( x_{1} )}} )Q_{m}}}} & (6)\end{matrix}$

In some implementations, a data driver (e.g. data driver 210 of FIG. 6)is configured to determine the initial position of a pixel and a finaldesired position of the pixel. From this information, a charge to beplaced on the pixel is calculated, and a voltage to be applied to themiddle layer to obtain this charge is calculated. These computations maybe done using formulas (3), (4), and (5) above. This voltage is thenoutput on the appropriate data line. The appropriate gate line isasserted for a time period long enough to charge the middle layer, butshort enough that the middle layer does not change positionsignificantly during the charging process. For example, in someimplementations, the appropriate gate line may be asserted from a timeperiod of about 1 μs to about 10 μs, while the response time of themiddle layer to application of a voltage may correspond to a period ofabout 50 μs to about 100 μs. Upon application of the charging voltage,the middle layer will then move to its final position.

FIG. 8 illustrates a portion of a driving circuit according to someimplementations configured according to these principles. As illustratedin FIG. 8, a data driver circuit may include a controller 840 configuredto control and coordinate driving of an array of display elements. Thecircuit of FIG. 8 also illustrates components of a pixel, which includethe fixed first layer 802, fixed second layer 804, movable third layer806, and switch S₁. As illustrated, the fixed second layer 804 isconnected to a ground voltage. As discussed above, in an alternativeimplementation, the fixed first layer 802 may be connected to ground,while the fixed second layer 804 may be connected to the voltage sourceV₀.

The controller 840 may receive image data indicating the final desiredposition of the middle layer. This image data may be numerical datadirectly defining the desired final position of the middle layer.Alternatively, the image data may define a desired color, luminance, orcombination thereof, and the controller 840 may generate a finalposition value from this image data. The controller 840 may also beconfigured to retain in memory the previous pixel position or receivethe previous pixel position through a buffer 842. Using the new desiredposition and the previously written position, the controller 840 maydetermine the voltage level V_(m) in the manner described above to applyto the movable third layer 806 through an output buffer 848. Thecontroller has additional outputs 850 that connect to respectiveadditional output drivers 848, one for each column of the array. Thus,for this implementation as well as the implementations described below,the operations may be performed in parallel on every pixel in a row of adisplay array.

FIG. 9 illustrates a flowchart of a method for controlling the positionof a movable conductive layer according to some implementations. Themethod 900 includes determining an initial position and a final positionof the movable conductive layer (such as movable third layer 806) withrespect to at least one of one or more fixed conductive layers (such asfixed first layer 802 and/or fixed second layer 804) as illustrated by ablock 902. A charging voltage may be determined based at least in parton the initial position and the final position as illustrated by a block904. The charging voltage may be applied to the movable conductive layerto move the movable conductive layer to a desired position asillustrated by a block 906.

The implementation of FIGS. 8 and 9 assumes that the spring constant Kand launch condition Δx_(L), are known and are substantially the samefor all of the pixels of the display array. When this is the case, thecalculation of the voltage V_(m) can be performed with these knownvalues and using only the initial pixel state and desired final pixelstate. When this is not the case, different pixels may require differentcharges to be moved to the same positions. Pixel by pixel adjustments tothe charge being applied in order to account for pixel by pixelvariations in K and Δx_(L), can be done in a variety of ways. Suchadjustments may include, among other methods, a sequential adjustment, acalibrated adjustment based on parameters individual pixels of thedisplay, or combinations thereof. A sequential adjustment method will bedescribed first, followed by a description of a calibrated parametersadjustment method.

In one implementation, position sensing circuitry for sensing the actualposition of the middle layer 806 can be incorporated into the drivingcircuitry. This is illustrated in FIG. 10, where FIG. 10 illustrates aportion of a display array driving and position sensing circuitaccording to some implementations. In FIG. 10, the controller also hasadditional input/output lines 850 for respective additional voltagesensors 922 and output drivers 848, one each for each column of thearray. Switch 51 connects the column drive line (such as at the outputof the output driver 848) to the mirror electrode 806 to drive themirror with the voltage V_(m), while the gate of S1 is driven by theCharge row drive line. The mirror electrode 806, when not driven by thecolumn drive line through switch 51, can be sampled by the sourcefollower transistor 932 which can be switched by transistor 930 toconnect it to (or isolate it from) the sense line 935 that is coupled tothe voltage sensor 922. In the implementations of FIG. 10, the senseline 935 is biased by a current source at the bottom of the column, asillustrated by transistor 937 (such as a thin-film transistor) having agate connected to a bias voltage V_(bb).

The approximate sense voltage V_(S) when the mirror is at position x isgiven by Equation 7:

$\begin{matrix}{{V_{s}(x)} = {{{\frac{( {d_{1} + x} )}{d_{1} + d_{2}}V_{0}}->x} = {{\frac{( {d_{1} + d_{2}} )}{V_{0}}V_{s}} - d_{1}}}} & (7)\end{matrix}$

Using the linear approximation of Q_(m) derived in Equation 3, the drivevoltage needed to drive the mirror to position x₁ from a currentposition x₀ may be given by Equation 8:

$\begin{matrix}{{V_{m}( {x_{0},x_{1}} )} \approx {{V_{S}( x_{0} )} - \frac{{K( {x_{1} - {\Delta\; x_{L}}} )}( {d_{1} + x_{1}} )( {d_{2} - x_{1}} )}{ɛ_{0}A_{P}V_{0}}}} & (8)\end{matrix}$

According to Equation 8, the voltage to apply to move the movable thirdlayer 806 from x₀ to x₁ may be determined using approximate or averagevalues for K and Δx_(L), which will be denoted as K and Δx_(L) . If thisdetermined voltage V_(m) is applied, and the spring constant is actuallyequal to K and the launch condition is actually given by Δx_(L) , thenthe mirror will move precisely to x₁. If, however, the spring constant Kand/or the launch condition Δx_(L), are different for this pixel thanthe calibrated initial values, then the movable third layer 806 may endat a position that is different from the desired position. Assuming thatthe values of K and Δx_(L), are different than the values K and Δx_(L) ,the actual position of the movable third layer 806 may be measured withthe voltage sensor 922 using Equation 7, and the applied charge may beadjusted based on the actual (incorrect) position and the desired finalposition x₁.

FIG. 11 illustrates an example of a method of sequential adjustment of amovable third layer 806 according to some implementations. Asillustrated in FIG. 11, during a first time period T1, a pixel positionmay correspond to the position during a previous frame. Following firsttime period T1, a sensing signal may be triggered to sense1 the voltageof the middle layer of the pixel. For example, with returned referenceto FIG. 10, during first sense time period T2, the gate driver Senseline may be asserted to connect the output of voltage sense transistor932 to the sense line 935 and thus to the voltage sensor 922 forobtaining a signal indicative of the voltage V_(S) applied to the gateof sense transistor 932 by mirror layer 806. Based on the sensed voltageV_(S) (used to determine current position), the desired final position,nominal spring stiffness K, and nominal launch condition Δx_(L) , avoltage V_(m) to apply to the movable third layer 806 may be determinedand applied to the data line via output buffer 848. Following firstsense time period T2, the gate driver sense line is de-asserted todisconnect the movable third layer 806 from the voltage sensor 922. Thegate driver charge line is then asserted, and the voltage V_(m) isapplied to the movable third layer 806 during first charge time periodT3.

Following first charge time period T3 and during transition time periodT4, the movable third layer 806 moves from the current position (such asx₀) to a next position (such as x₁) based on the applied voltage V_(m)and corresponding charge Q_(m). As illustrated, transition time periodT4 may be substantially greater than time periods T2 and T3. In someimplementations, during transition time period T4, a controller (e.g.controller 840) may be configured to sequentially write data to otherrows of pixels in the display 30 using the same procedure. For example,following the application of the voltage V_(m) during charge time periodT3, the controller 840 may be configured to sense a current position ofpixels in a next row, and apply a determined voltage based on the sensedposition and a desired position of the pixels in the next row. In thisway, data may be written to the display 30 sequentially while themovable layers 806 transition from a current position to a nextposition. Transition time period T4 may correspond to a duration thatallows data to be written to all rows of a display 30, or a section ofthe display 30, prior to returning to the first row.

Following the transition time period T4, the current position of themovable third layer 806 may be offset from the desired position. Thecurrent position may be determined based on a second measurement of thevoltage V_(S) of the movable third layer 806 during a second sense timeperiod T5 in the same manner as is done in time period T2. Based on thismeasured position and the desired final position x₁, a new voltage V_(m)may be derived which corrects this initial error in the position of themovable layer 806.

The determination of the voltage V_(m) applied during the second chargetime T6 may be implemented as shown in Equation 9:

$\begin{matrix}{{V_{C}( {x_{1},x_{F}} )} =  {{V_{S}( x_{F} )} + {( \frac{1}{{C_{1}( x_{F} )} + {C_{2}( x_{F} )}} ){Q_{m}( {\overset{\_}{K},\overset{\_}{\Delta\; x_{L}},x_{F}} )}} + {( {x_{F} - x_{1}} )\frac{\partial{Qm}}{\partial x}}} |_{x = x_{1}}} & (9)\end{matrix}$

The position of the movable third layer 806 may be sequentially adjustedduring the same frame time. Further, as discussed above, other rows ofthe display may be written while the movable third layer 806 of a pixelin a given row transitions to a position corresponding to the appliedvoltage V_(m). In some implementations, for a frame rate of 15 Hz, eachpixel may be adjusted at least twice within 1/15^(th) of a second.

Another method of adjusting the position of the movable third layer 806which may be used alternatively to the sequential adjustment method, orin combination with the sequential adjustment method, is a specificallycalibrated placement of the movable third layer 806 based on separatemeasurements of the mechanical parameters K and Δx_(L), associated witheach pixel of an array. An example of calibrated adjustment will bedescribed with reference to FIGS. 12-15.

In some implementations, the calibration adjustment method may includean accurate measurement of independent parameters related to each of thepixels and a determination of a voltage V_(m) based on the measuredparameters. The measured parameters may include the launch positionΔx_(L), and the spring stiffness K of each pixel.

FIG. 12 illustrates a portion of a display array driving and sensingcircuit including circuitry for testing pixel characteristics. In thisimplementation, the gate driver includes an additional test line outputcoupled to the gates of n-type transistors 1022, 1024, and p-typetransistor 1026. When the gate driver Test line is asserted, transistor1022 connects movable layer 806 to ground and transistor 1026 connectsfixed layer 802 to ground. When the Test line is de-asserted, themovable layer 806 is de-coupled from ground, and fixed layer 802 iscoupled to V₀ through p-type transistor 1024. These connections, alongwith the sensing and driving circuits described above, can be used todetermine individual values for K and Δx_(L), as described below withreference to FIGS. 13 and 14. The values determined for each pixel maybe stored in a look-up table (LUT) 1030 in the driver circuit and usedto calculate correct values for V_(m) for each pixel rather than relyingon nominal or average values K and Δx_(L) . This may eliminate the needfor the sequential correction procedure described above with referenceto FIGS. 10 and 11.

FIG. 13 is a flowchart of a method of determining the launch conditionΔx_(L), according to some implementations. The method 1100 may includeconnecting a fixed first layer 802 to a ground voltage as illustrated bya block 1102. For example, with returned reference to FIG. 12, the gatedriver Test line may be asserted, turning transistor 1024 off and 1026on, thus connecting the fixed first layer 802 to ground. The movablethird layer 806 may then be connected to ground as illustrated by ablock 1104 (such as by turning on transistor 1022 with the same Testline assertion). This removes all charge from the layers of the pixel,and the middle layer 806 will move to a position of purely mechanicalequilibrium. As illustrated by a block 1106, the movable third layer 806may then be disconnected from ground such that the movable third layer806 is in a floating state, and the first fixed layer 802 may beconnected to bias voltage V₀ as illustrated by a block 1108. Both ofthese acts may be accomplished at the same time by de-asserting the Testline. At a block 1110, the voltage V_(S) of the movable third layer 806may be measured (such as by asserting the gate driver Sense line). Thevoltage V_(S) measured in this condition is proportional to the launchcondition Δx_(L), since any deviation in position of the movable thirdlayer 806 will correspond to a fabrication induced mechanical bias, orthe like. At a block 1112 the launch condition Δx_(L), of the movablethird layer may be determined based on the voltage V_(S) which isrelated to the position of the middle layer under these conditions. Insome implementations, the determined launch condition Δx_(L), may besaved in a look-up-table (such as LUT 1030) as discussed above withreference to FIG. 12.

FIG. 14 is a flowchart of a method of determining the spring stiffness Kfor a pixel according to some implementations. The method 1200 includesconnecting the fixed first layer 802 to ground as illustrated by a block1202, and connecting the movable third layer 806 to ground asillustrated by a block 1204, which may be done as described above withrespect to FIGS. 12 and 13. A calibration voltage V_(Ca1) as illustratedby a block 1206 may then be applied to the data line. The calibrationvoltage V_(Ca1) may correspond to a voltage level (such as V₀/2) thatcorresponds to a movable third layer 806 charge at a quiescent positioncapacitance which is tolerant to launch condition variations. At a block1208, the movable third layer 806 may be connected to the calibrationvoltage V_(Ca1) by, for example, asserting the gate driver Charge lineof FIG. 12. As illustrated by a block 1210, the movable third layer 806may then be disconnected from the voltage signal V_(Ca1) such that themovable third layer 806 is in a floating state (such as by de-assertingthe Charge line). At a block 1212, the fixed first layer 802 may beconnected to the bias voltage V₀. The bias voltage V₀ is applied to thefixed first layer 802 for a time period until the movable third layer806 reaches an equilibrium position as illustrated by a block 1214. At ablock 1216, the voltage V_(S) of the movable third layer 806 may bemeasured (such as by asserting the gate driver Sense line). The voltageV_(S) measured in this condition is related to the spring stiffness K,and at a block 1218 the spring stiffness K of the movable third layermay be determined based on the voltage V_(S). In some implementations,the determined spring stiffness K may be saved in a look-up-table (suchas LUT 1030) as discussed above with reference to FIG. 12.

Based on the measurements of the launch condition Δx_(L), the springstiffness K, and the values of the previous pixel position and thedesired pixel position, the voltage V_(m) to be applied to the movablethird layer 806 for each pixel individually may be determined. FIG. 15is a flowchart of a calibrated adjustment method 1300 according to someimplementations. At a block 1304, pixel specific parameters includingthe launch condition Δx_(L), spring stiffness K, previous position, anddesired position may be received and/or determined. For example, thelaunch condition Δx_(L), and spring stiffness K may be determinedaccording to measurements as discussed with reference to FIGS. 11 and12, respectively and which have been stored in LUT 1030 of FIG. 12. At ablock 1306, a voltage level V_(m) is determined based at least in parton the parameters. At a block 1308, the movable third layer 1308 may beconnected to the data line (such as by asserting the gate driver Chargeline). As a result, the movable third layer may be accurately positionedby application of the voltage V_(m).

In the implementation described above, the LUT 1030 stores the set ofpixel parameters Δx_(L), and K previously measured for each pixel, andthese are retrieved to derive a V_(m) that will move the layer 806 froma current position to a desired final position. In some implementations,the LUT may store level V_(m) values directly, which are accessed by thevalues for the initial position and desired final position. In theseimplementations, a table of level V_(m) values may be individuallyprovided for each pixel, where the level V_(m) values in each table arederived based on the specific Δx_(L), and K values for that pixel.

In the above described implementations, the voltage V_(m) applied to themovable third layer 806 is a variable analog voltage level output by thedata driver. In alternative implementations, the voltage applied mayinclude a pulse or series of pulses. A pulsed voltage signal may includea temporally modulated voltage signal to induce the desired charge Q_(m)to the movable middle layer 806 using one or more fixed referencevoltages. FIG. 16 illustrates an example of a circuit configured togenerate a pulsed voltage signal for inducing charge to the movablethird layer 806. As illustrated in FIG. 16, a row select signal 1402 maybe used to selectively enable the connection of the movable third layer806 to a first transistor 1412 and a second transistor 1414. The secondtransistor 1414 is biased to a constant voltage level (such as V₀) andthe first transistor is biased to ground. The first transistor 1412 andthe second transistor 1414 are turned on/off in sequence through acorresponding first column electrode 1404 connected to the gate of thefirst transistor 1412, and a second column electrode 1406 connected tothe gate of the second transistor 1414. One of the voltage V₀ and groundis applied in according to a pulsed waveform through a third transistor1410 having an output connected to the movable third layer 806. Based onthe configuration of FIG. 16, the electrodes 1404 and 1406 switchbetween binary values whose exact values are not critical to theoperation of the charge injection process.

FIG. 17 illustrates another example of a circuit configured to generatea pulsed voltage signal for inducing charge to the movable third layer806. As illustrated in FIG. 17, a gate of the first transistor isconnected to a first select signal 1504, while a gate of the secondtransistor is connected to a second select signal 1506. As in FIG. 16,the first transistor 1412 is biased to a constant voltage level, whilethe second transistor is biased to ground. A single electrode 1520 isconfigured to connect an output of one of the first transistor 1412 andthe second transistor 1414 to the third transistor 1510. As a result,the single column electrode 1520 switches between V₀ and ground insequence through operation of the first transistor 1412 and the secondtransistor 1414. The row select signal 1402 enables the connection ofthe movable third layer 806 to the output of the third transistor 1510.

FIGS. 18A and 18B show examples of system block diagrams illustrating adisplay device 40 that includes a plurality of interferometricmodulators. The display device 40 can be, for example, a cellular ormobile telephone. However, the same components of the display device 40or slight variations thereof are also illustrative of various types ofdisplay devices such as televisions, e-readers and portable mediaplayers.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 can be formed from any of a variety of manufacturing processes,including injection molding, and vacuum forming. In addition, thehousing 41 may be made from any of a variety of materials, including,but not limited to: plastic, metal, glass, rubber, and ceramic, or acombination thereof. The housing 41 can include removable portions (notshown) that may be interchanged with other removable portions ofdifferent color, or containing different logos, pictures, or symbols.

The display 30 may be any of a variety of displays, including abi-stable or analog display, as described herein. The display 30 alsocan be configured to include a flat-panel display, such as plasma, EL,OLED, STN LCD, or TFT LCD, or a non-flat-panel display, such as a CRT orother tube device. In addition, the display 30 can include aninterferometric modulator display, as described herein.

The components of the display device 40 are schematically illustrated inFIG. 18B. The display device 40 includes a housing 41 and can includeadditional components at least partially enclosed therein. For example,the display device 40 includes a network interface 27 that includes anantenna 43 which is coupled to a transceiver 47. The transceiver 47 isconnected to a processor 21, which is connected to conditioning hardware52. The conditioning hardware 52 may be configured to condition a signal(such as by filtering a signal). The conditioning hardware 52 isconnected to a speaker 45 and a microphone 46. The processor 21 is alsoconnected to an input device 48 and a driver controller 29. The drivercontroller 29 is coupled to a frame buffer 28, and to an array driver22, which in turn is coupled to a display array 30. A power supply 50can provide power to all components as required by the particulardisplay device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the display device 40 can communicate with one or more devicesover a network. The network interface 27 also may have some processingcapabilities to relieve, data processing requirements of othercomponents, such as of the processor 21. The antenna 43 can transmit andreceive signals. In some implementations, the antenna 43 transmits andreceives RF signals according to the IEEE 16.11 standard, including IEEE16.11(a), (b), or (g), or the IEEE 802.11 standard, including IEEE802.11a, b, g or n. In some other implementations, the antenna 43transmits and receives RF signals according to the BLUETOOTH standard.In the case of a cellular telephone, the antenna 43 is designed toreceive code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), GlobalSystem for Mobile communications (GSM), GSM/General Packet Radio Service(GPRS), Enhanced Data GSM Environment (EDGE), Terrestrial Trunked Radio(TETRA), Wideband-CDMA (W-CDMA), Evolution Data Optimized (EV-DO),1xEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access (HSPA), HighSpeed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access(HSUPA), Evolved High Speed Packet Access (HSPA+), Long Term Evolution(LTE), AMPS, or other known signals that are used to communicate withina wireless network, such as a system utilizing 3G or 4G technology. Thetransceiver 47 can pre-process the signals received from the antenna 43so that they may be received by and further manipulated by the processor21. The transceiver 47 also can process signals received from theprocessor 21 so that they may be transmitted from the display device 40via the antenna 43.

In some implementations, the transceiver 47 can be replaced by areceiver. In addition, the network interface 27 can be replaced by animage source, which can store or generate image data to be sent to theprocessor 21. The processor 21 can control the overall operation of thedisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 can send the processeddata to the driver controller 29 or to the frame buffer 28 for storage.Raw data typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

The processor 21 can include a microcontroller, CPU, or logic unit tocontrol operation of the display device 40. The conditioning hardware 52may include amplifiers and filters for transmitting signals to thespeaker 45, and for receiving signals from the microphone 46. Theconditioning hardware 52 may be discrete components within the displaydevice 40, or may be incorporated within the processor 21 or othercomponents.

The driver controller 29 can take the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and can re-format the raw image data appropriately for highspeed transmission to the array driver 22. In some implementations, thedriver controller 29 may correspond to the controller 840 as discussedabove with reference to FIGS. 10 and 12. In some implementations, thedriver controller 29 can re-format the raw image data into a data flowhaving a raster-like format, such that it has a time order suitable forscanning across the display array 30. Then the driver controller 29sends the formatted information to the array driver 22. In someimplementations, the array driver 22 may include the gate drive and oneor more of output drivers 848 as described above with reference to FIGS.10 and 12. Although a driver controller 29, such as an LCD controller,is often associated with the system processor 21 as a stand-aloneIntegrated Circuit (IC), such controllers may be implemented in manyways. For example, controllers may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

The array driver 22 can receive the formatted information from thedriver controller 29 and can re-format the video data into a parallelset of waveforms that are applied many times per second to the hundreds,and sometimes thousands (or more), of leads coming from the display'sx-y matrix of pixels.

In some implementations, the driver controller 29, the array driver 22,and the display array 30 are appropriate for any of the types ofdisplays described herein. For example, the driver controller 29 can bea conventional display controller or a bi-stable display controller(such as an IMOD controller). Additionally, the array driver 22 can be aconventional driver or a bi-stable display driver (such as an IMODdisplay driver). Moreover, the display array 30 can be a conventionaldisplay array or a bi-stable display array (such as a display includingan array of IMODs). In some implementations, the driver controller 29can be integrated with the array driver 22. Such an implementation iscommon in highly integrated systems such as cellular phones, watches andother small-area displays.

The array driver 22 may be implemented on a separate substrate or usinga separate chip from the display array 30. The voltage sources V₀ andV_(m) discussed above may also be located remotely from theinterferometric modulator. For example, one or both of the voltagesources V₀ and V_(m) may be implemented in the array driver 22, and/orone or both of the voltage sources V₀ and V_(m) could be controlled orreceive instructions from the array driver 22, the driver controller 29,or the processor 21.

In some implementations, the input device 48 can be configured to allowa user to control the operation of the display device 40. The inputdevice 48 can include a keypad, such as a QWERTY keyboard or a telephonekeypad, a button, a switch, a rocker, a touch-sensitive screen, or apressure- or heat-sensitive membrane. The microphone 46 can beconfigured as an input device for the display device 40. In someimplementations, voice commands through the microphone 46 can be usedfor controlling operations of the display device 40.

The power supply 50 can include a variety of energy storage devices asare well known in the art. For example, the power supply 50 can be arechargeable battery, such as a nickel-cadmium battery or a lithium-ionbattery. The power supply 50 also can be a renewable energy source, acapacitor, or a solar cell, including a plastic solar cell or solar-cellpaint. The power supply 50 also can be configured to receive power froma wall outlet.

In some implementations, control programmability resides in the drivercontroller 29 which can be located in several places in the electronicdisplay system. In some other implementations, control programmabilityresides in the array driver 22. The above-described optimization may beimplemented in any number of hardware and/or software components and invarious configurations.

FIG. 19 is an example of a schematic exploded perspective view of theelectronic device 40 of FIGS. 16A and 16B according to oneimplementation. The illustrated electronic device 40 includes a housing41 that has a recess 41 a for a display array 30. The electronic device40 also includes a processor 21 on the bottom of the recess 41 a of thehousing 41. The processor 21 can include a connector 21 a for datacommunication with the display array 30. The electronic device 40 alsocan include other components, at least a portion of which is inside thehousing 41. The other components can include, but are not limited to, anetworking interface, a driver controller, an input device, a powersupply, conditioning hardware, a frame buffer, a speaker, and amicrophone, as described earlier in connection with FIG. 18B.

As discussed above, since the charge of movable third layer 806, andcorresponding position of the movable third layer 806 is determined inresponse to supplied voltages V_(m), a table or other data structure maybe created to correlate the supplied voltages V_(m) to the actualposition of the movable third layer 806. In this way, the voltage to beapplied to the movable third layer 806 may be retrieved based on adesired position via the look-up table during subsequent operationsinstead of calculated, thereby conserving power. Further, the table mayallow drive circuitry which supplies the voltages V_(m) to adjust drivevoltages so as to correctly drive the movable third layer 806 to adesired position. The table may be any structure or compilation of datain which correlated values may be stored. The table may be stored in avolatile or non-volatile memory, for example in a storage device or unit(not shown) implemented in the display device 40, discussed above. Thevoltage sensing functions and/or writing of data to the table may beperformed by a processor, for example by the processor 21 of the displaydevice 40. In some embodiments, the processor 21 includes storage forsome or all of the table values.

The display array 30 can include a display array assembly 110, abackplate 120, and a flexible electrical cable 130. The display arrayassembly 110 and the backplate 120 can be attached to each other, using,for example, a sealant.

The display array assembly 110 can include a display region 101 and aperipheral region 102. The peripheral region 102 surrounds the displayregion 101 when viewed from above the display array assembly 110. Thedisplay array assembly 110 also includes an array of display elementspositioned and oriented to display images through the display region101. The display elements can be arranged in a matrix form. In someimplementations, each of the display elements can be an interferometricmodulator. Also, in some implementations, the term “display element” maybe referred to as a “pixel.”

The backplate 120 may cover substantially the entire back surface of thedisplay array assembly 110. The backplate 120 can be formed from, forexample, glass, a polymeric material, a metallic material, a ceramicmaterial, a semiconductor material, or a combination of two or more ofthe foregoing materials, in addition to other similar materials. Thebackplate 120 can include one or more layers of the same or differentmaterials. The backplate 120 also can include various components atleast partially embedded therein or mounted thereon. Examples of suchcomponents include, but are not limited to, a driver controller, arraydrivers (for example, a data driver and a scan driver), routing lines(for example, data lines and gate lines), switching circuits, processors(for example, an image data processing processor) and interconnects.

The flexible electrical cable 130 serves to provide data communicationchannels between the display array 30 and other components (for example,the processor 21) of the electronic device 40. The flexible electricalcable 130 can extend from one or more components of the display arrayassembly 110, or from the backplate 120. The flexible electrical cable130 can include a plurality of conductive wires extending parallel toone another, and a connector 130 a that can be connected to theconnector 21 a of the processor 21 or any other component of theelectronic device 40.

The various illustrative logics, logical blocks, modules, circuits andalgorithm steps described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and steps described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular steps and methods maybe performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The steps of a method or algorithm disclosedherein may be implemented in a processor-executable software modulewhich may reside on a computer-readable medium. Computer-readable mediaincludes both computer storage media and communication media includingany medium that can be enabled to transfer a computer program from oneplace to another. A storage media may be any available media that may beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media may include RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that may be used to store desired programcode in the form of instructions or data structures and that may beaccessed by a computer. Also, any connection can be properly termed acomputer-readable medium. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk, and blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.Additionally, a person having ordinary skill in the art will readilyappreciate, the terms “upper” and “lower” are sometimes used for ease ofdescribing the figures, and indicate relative positions corresponding tothe orientation of the figure on a properly oriented page, and may notreflect the proper orientation of the IMOD as implemented.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flow diagram. However, other operations thatare not depicted can be incorporated in the example processes that areschematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other implementations are within the scope of thefollowing claims. In some cases, the actions recited in the claims canbe performed in a different order and still achieve desirable results.

What is claimed is:
 1. An apparatus for driving a display element, thedisplay element including a movable conductive layer and one or morefixed conductive layers, the apparatus comprising: a circuit configuredto determine an initial position of the movable conductive layer withrespect to at least one of the one or more fixed conductive layers, thecircuit comprising at least one transistor, the at least one transistorhaving its gate coupled to the moveable layer; and a controllerconfigured to: determine a charging voltage based at least in part onthe initial position; and apply the charging voltage to the movableconductive layer.
 2. The apparatus as recited in claim 1, wherein thecharging voltage is determined based at least in part on a target finalposition of the movable conductive layer.
 3. The apparatus as recited inclaim 1, wherein the controller is capable of applying the chargingvoltage for a period of time that is less than a mechanical responsetime of the movable conductive layer.
 4. The apparatus as recited inclaim 3, comprising a switch capable of isolating the movable conductivelayer from the charging voltage prior to the movable conductive layersignificantly responding to the applied voltage.
 5. The apparatus asrecited in claim 4, wherein the switch comprises a metal oxide thin filmtransistor.
 6. The apparatus as recited in claim 5, wherein the metaloxide thin film transistor comprises an indium gallium zinc oxideswitch.
 7. The apparatus as recited in claim 6, wherein the circuitcapable of determining an initial position of the movable conductivelayer includes a voltage sensor.
 8. The apparatus as recited in claim 7,wherein the voltage sensor is capable of sensing the position of themovable conductive layer subsequent to applying the charging voltage,and wherein the controller is capable of: determining a correctivevoltage based at least in part on the position sensed subsequent toapplying the charging voltage; and applying the determined correctivevoltage to the movable conductive layer.
 9. The apparatus as recited inclaim 5, further comprising applying a bias voltage across the first andsecond fixed conductive layers.
 10. The apparatus as recited in claim 1,wherein the movable conductive layer and the one or more fixedconductive layers are included in a first display element, the firstdisplay element being disposed in an array of display elements.
 11. Theapparatus as recited in claim 10, wherein the controller is capable ofdetermining a charging voltage to apply to each of a plurality of thedisplay elements in the array using a value of a mechanical propertythat is common to the plurality of the display elements.
 12. Theapparatus as recited in claim 1, further comprising a lookup tablehaving values corresponding to each of the plurality of displayelements, and wherein the controller is capable of determining thecharging voltage for each display element using the stored values. 13.The apparatus as recited in claim 12, wherein the controller is capableof determining a charging voltage to apply to each of a plurality of thedisplay elements in the array based at least in part on respectivemechanical properties of each of the plurality of display elements. 14.The apparatus as recited in claim 1, wherein the controller is capableof determining one or both of a spring constant or a launch bias of themovable conductive layer.
 15. The apparatus as recited in claim 1,wherein the movable conductive layer is disposed between the first andsecond fixed conductive layers.
 16. The apparatus as recited in claim 1,further comprising: a display, the display element being one in an arrayof display elements of the display; a processor that is capable ofcommunicating with the display, the processor being configured toprocess image data; and a memory device that is capable of communicatingwith the processor.
 17. The apparatus as recited in claim 16,additionally including a driver circuit that is capable of sending atleast one signal to the display, and wherein a controller is capable ofsending at least a portion of the image data to the driver circuit. 18.The apparatus as recited in claim 16, further comprising: an imagesource module capable of sending the image data to the processor. 19.The apparatus as recited in claim 18, wherein the image source moduleincludes at least one of a receiver, transceiver, and transmitter. 20.The apparatus as recited in claim 16, further comprising: an inputdevice capable of receiving input data and to communicate the input datato the processor.
 21. A method of positioning a movable conductive layerthat is movable with respect to one or more fixed conductive layers in adisplay, the method comprising: applying a voltage to the one or morefixed conductive layers in the display; placing the movable conductivelayer at an initial position, the initial position corresponding to afirst position of the movable conductive layer; sensing a voltage on themovable conductive layer at the initial position; determining theinitial position of the movable conductive layer with respect to atleast one of the one or more fixed conductive layers based at least inpart on the sensed voltage; determining a final position of the movableconductive layer with respect to at least one of the one or more fixedconductive layers, the final position corresponding to an immediatelysubsequent second position at which the movable conductive layer is tobe placed after application of the charging voltage; determining thecharging voltage based on the initial position and the final position;and applying the charging voltage to the movable conductive layer at theinitial position.
 22. The method as recited in claim 21, wherein thecharging voltage is applied for a period of time that is less than amechanical response time of the movable conductive layer.
 23. The methodas recited in claim 21, further comprising sensing the position of themovable conductive layer subsequent to applying the charging voltage,determining a corrective voltage based at least in part on the positionsensed subsequent to applying the determined voltage, and applying thedetermined corrective voltage to the movable conductive layer.
 24. Anapparatus for driving a display including a movable conductive layer andone or more fixed conductive layers, the apparatus comprising; means forapplying a voltage to the one or more fixed conductive layers in thedisplay; means for placing the movable conductive layer at an initialposition, the initial position corresponding to a first position of themovable conductive layer; means for sensing a voltage on the movableconductive layer at the initial position; means for determining theinitial position of the movable conductive layer with respect to atleast one of the one or more fixed conductive layers based at least inpart on the sensed voltage; means for determining a final position ofthe movable conductive layer with respect to at least one of the one ormore fixed conductive layers, the final position corresponding to animmediately subsequent second position at which the moveable conductivelayer is to be placed after application of the charging voltage; andmeans for determining the charging voltage based on the initial positionand the final position, the means for applying further configured toapply the charging voltage to the movable conductive layer at theinitial position.
 25. The apparatus as recited in claim 24, wherein themeans for determining the initial position and the means for determininga final position comprise a voltage sensor, the means for determining acharging voltage comprises a controller, and the means for applying thecharging voltage comprises a controller.
 26. The apparatus as recited inclaim 24, further comprising means for isolating the movable conductivelayer from the charging voltage prior to the movable conductive layerresponding to the applied voltage.
 27. The apparatus as recited in claim26, wherein the means for isolating the movable conductive layercomprises a switch.
 28. A computer program product for positioning amovable conductive layer that is movable with respect to one or morefixed conductive layers in a display, the computer program productcomprising: a non-transitory computer-readable medium having storedthereon code for causing processing circuitry to: apply a voltage to theone or more fixed conductive layers in the display; place the movableconductive layer at an initial position, the initial positioncorresponding to a first position of the movable conductive layer; sensea voltage on the movable conductive layer at the initial position;determine the initial position of the movable conductive layer withrespect to at least one of the one or more fixed conductive layers basedat least in part on the sensed voltage; determine a target finalposition of the movable conductive layer with respect to at least one ofthe one or more fixed conductive layers, the target final positioncorresponding to an immediately subsequent second position at which themovable conductive layer is to be placed after application of thecharging voltage; determine the charging voltage based on the initialposition and the target final position; and apply the charging voltageto the movable conductive layer at the initial position.
 29. Thecomputer program product as recited in claim 28, wherein the chargingvoltage is applied for a period of time that is less than a mechanicalresponse time of the movable conductive layer.